1. Field of the Invention
This invention relates to an electrode for hydrogen generation having a low hydrogen overvoltage to be used for electrolysis of aqueous solutions typically including brine.
2. Description of the Related Art
It is a very important challenge to reduce the energy consumption rate of electrolysis of brine. While the energy consumption rate of ion-exchange membrane electrolysis is relatively low if compared with other electrolytic processes, there is a demand for techniques that can further reduce the energy consumption rate of ion-exchange membrane electrolysis.
The power consumption rate of ion-exchange membrane electrolysis depends on various factors such as the structure of the electrolyzer including an anode, an ion-exchange membrane and a cathode. The particular object of the present invention is to reduce the energy consumption rate of electrolysis by reducing the hydrogen overvoltage at the electrode for hydrogen generation that operates as cathode.
Many proposals have already been made for electrodes for hydrogen generation to be used for electrolysis of aqueous solutions including brine. Such proposals include those for using an electrode having an electrode catalyst coating of nickel, cobalt, a platinum group metal or an oxide or an alloy of any of such metals formed on a metal base member.
Electrodes for hydrogen generation are required to show a low hydrogen overvoltage and additionally not to contaminate the ion-exchange membrane with the heavy metal eluted from the electrode catalyst coating formed on the surface of the electrode even when the electrode is operated in a state where an ion-exchange membrane and the electrode for hydrogen generation are held in contact with each other. Still additionally, the ion-exchange membrane is required to be undamaged when it is brought into contact with the surface of the electrode catalyst layer.
WO 2003/078694 proposes to form a coating layer of an electrode catalyst by applying a mixture of ruthenium chloride, cerium chloride and oxalic acid to the surface of a conductive base member and thermally decomposing it.
When forming an electrode catalyst layer by thermally decomposition, it is a common practice to use a substance whose metal component shows a high solubility and that is decomposed by thermally decomposition and volatilized so as not to remain in the electrode catalyst layer for the solution containing the metal compound that is to be applied onto the conductive base member. In the case of using a platinum group metal compound, it is a common practice to utilize a hydrochloric acid solution of chloride of the metal. However, no attention has been paid to date to the type of the salt of the metal compound.
For example, according to the above-cited WO 2003/078694, ruthenium chloride and cerium oxalate are introduced into the electrode catalyst coating layer of the electrode for hydrogen generation respectively as ruthenium and cerium. However, the fall of the electric potential is not satisfactory for electrolysis with a high electric current density.
Thus, it is the object of the present invention to provide an electrode for hydrogen generation that can maintain a low hydrogen overvoltage for a long period of time in electrolysis using a high current density and is highly catalysis-active relative to hydrogen generation reactions, while it can satisfactorily prevent the ion-exchange membrane from being contaminated by the eluted heavy metal even when the ion-exchange membrane is brought into contact with the cathode in the electrolyzer and excellently shows a uniform current distribution on the electrode surface.